Object-oriented Software in Ada 95

Tasks 293
Likewise, the task Task_Is_Prime in the package Pack_Is_A_Prime receives and delivers data to
another thread of control.
package body Pack_Is_A_Prime is
task body Task_Is_Prime is --Implementation
Prime : Positive;
Answer: Boolean := True;
begin
accept Start( P:in Positive ) do --Factorial
Prime := P;
end Start;
for I in 2 .. Prime-1 loop --Calculate
if Prime rem I = 0 then
Answer := False; exit;
end if;
end loop;
accept Finish( Result:out Boolean ) do --Return answer
Result := Answer;
end Finish;
end Task_Is_Prime;
end Pack_Is_A_Prime;
20.2 Parameters to a task type
In the previous example, the rendezvous Start is used to pass initial values to the task. This can be done
explicitly, when the task is created by using a discriminated task type. However, the discriminant must be a
discrete type or access type. For example, the specification of the task Task_Factorial can be defined as
follows:
package Pack_Factorial is
task type Task_Factorial(F:Positive) is --Specification
entry Finish( Result:out Positive ); --Rendezvous
end Task_Factorial;
end Pack_Factorial;
Then an instance of the task can be elaborated as follows:
Thread_1 : Task_Factorial(7);
--Task is
The body of the task type is now:
package body Pack_Factorial is
task body Task_Factorial is --Implementation
Answer : Positive := 1;
begin
for I in 2 .. F loop
--Calculate
Answer := Answer * I;
end loop;
accept Finish( Result:out Positive ) do --Return answer
Result := Answer;
end Finish;
end Task_Factorial;
end Pack_Factorial;
Note:
The discriminant to the task type is not specified in the body.
© M A Smith - May not be reproduced without permission